1. Field of the invention
The present invention relates to DD motors (direct drive motors) used in magnetic disk drives for driving magnetic disks.
2. Related art
As shown in FIGS. 4 and 5, a conventional magnetic disk (floppy disk) drive DD motor is designed to be disposed on a lower surface of a frame of a magnetic disk drive (the surface opposite to the surface on the magnetic disk side).
That is, in FIGS. 4 and 5, a DD motor 1 has a printed board 3 disposed on a frame 2, a spindle shaft 4, a rotor 5, and a disk table 6.
The printed board 3 has a coil (not shown) formed of a conductive pattern on a surface thereof.
The spindle shaft 4 is not only inserted into a through hole formed in the frame 2 and the printed board 3, but also supported by a bearing 4a so as to be vertical and rotatable with respect to the frame 2.
The rotor 5 is set into the lower end portion of the spindle shaft 4, and has a circular rotor case 5a that has a flange portion extending toward the frame 2 from the circumferential edge of the rotor case, a ringlike rotor magnet 5b mounted on the frame 2 side of the rotor case 5a, and a rotational direction detecting index magnet 5c mounted on the outer circumferential surface of the rotor case 5a.
The disk table 6 is disposed opposite to the rotor 5 with the frame 2 interposed therebetween, and is mounted onto an upper end portion of the spindle shaft 4. The upper surface of the disk table 6 protrudes, and not only supports a magnetic disk 7, but also has a chucking plate 8 formed of a magnetic substance for chucking the magnetic disk 7. As shown in FIG. 5, one end of the chucking arm 9 for chucking the magnetic disk 7 is oscillatably supported on the circumferential edge of the upper surface of the disk table 6 by a support pin 9a. A roller 9b engageable with a window 7b of a hub 7a of the magnetic disk 7 is rotatably disposed on the other end of the chucking arm 9.
According to the thus constructed magnetic disk drive DD motor 1, the magnetic disk 7 is fixed and held on the disk table 6 while disposed on the disk table 6 and chucked by the chucking plate 8.
When a drive current is applied to the coil formed on the printed board 3 under this condition, a magnetic field generated in the coil acts mutually with a magnetic field of the rotor magnet 5b of the rotor 5, so that the rotor 5 rotates together with the spindle shaft 4. Then, the chucking roller 9b of the chucking arm 9 engages with the window 7b of the hub 7a of the magnetic disk 7, so that the magnetic disk 7 is driven to rotate.
However, in the thus constructed magnetic disk drive DD motor 1, the rotor 5 and the disk table 6 are not only formed in separate pieces, but also mounted onto the spindle shaft 4 so as to interpose the frame 2 therebetween.
Further, the rotor 5 is not only set into the spindle shaft 4 by fixing screws, but also has the rotor magnet 5b and the index magnet 5c, which are formed independently of each other, attached thereto by an adhesive or the like.
Still further, the chucking plate 8 is mounted on the disk table 6 with an adhesive or the like, and one end of the chucking arm 9 for chucking the magnetic disk 7 is supported on the disk table 6 with the support pin 9a so as to be oscillatable, e.g., by self-locking or the like.
Therefore, the number of parts of the DD motor 1 as a whole is increased, which in turn has imposed the problem of elevated parts and assembling costs.